Static displacement is, but were dealing with a running engines so I'm talking Dynamic displacement, what an engine displaces every minute.
Fuel and it's volume of air has a potential energy an engine only gonna use a % of that potential energy to make hp.
What is displacement in our case, but volume/weight of air, the engine measure displacement x ve% moves that much air per revolution, more revolution more air being displaced eg.. A 360 moves 0.104 cfm (cfm = volume of air per minute or a displacement of air per minute) per revolution more revolutions more displacement. A 360 @ 5000 rpm = 521 cfm a 360 @ 6000 rpm = 625 cfm at 100% VE. A 340 @ 5316 rpm = 521 cfm a 340 @ 6378 rpm = 625 cfm same dynamic displacement and yes sure you also spin the 360 more to.
I guess, makes perfect sense to me :)
